Faults in electrical systems are of a variety of different types. For example, permanent faults are faults that physically always exist in the system. Intermittent faults are faults that physically exist at one moment, but may disappear at another moment. Various approaches have been used to detect the permanent faults only.
Intermittent faults do not produce post-fault steady-state behavior for very long. Instead, these faults quickly disappear shortly after a short-lived transient period without reaching a steady state. In fact, these faults may last only about one cycle length of time. For example, underground insulation breakdown intermittent faults (for underground cable) or overhead power lines typically last less than one cycle, most often for about ½ cycle or less. These sub-cycle faults, which may lead to permanent faults, need to be located before they can develop into permanent faults.
As mentioned, various approaches have been used to detect and locate permanent faults. Unfortunately, these conventional fault location approaches are incapable of locating sub-cycle faults. In fact and in most cases, sub-cycle faults are simply ignored by previous approaches. Therefore, determination of distance to such a sub-cycle intermittent fault is not even attempted.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein.